The present invention relates to devices for performing micro-surgical procedures in the posterior portion of the eye. More particularly, the present invention relates to a high-speed pneumatically driven vitreous cutter.
The instrument most commonly used, and generally preferred, for vitreous surgery is a pneumatically-operated axial guillotine cutter. A typical pneumatically-operated guillotine cutter has a handpiece that includes a needle with a cutting/aspiration port located near the needle""s distal end. The handpiece receives pneumatic power from a vitreoretinal surgical system (or console). Often, the system also provides aspiration and illumination functions.
Although numerous improvements have been made over the years, the fundamental aspects of vitreous cutters are known and taught by O""Malley and Heintz in U.S. Pat. Nos. 3,815,604 and 3,884,238, respectively. In its modern form, the axial guillotine cutter is relatively small, lightweight, durable, cheap, and exhibits excellent cutting characteristics.
One negative aspect of guillotine cutters, whether pneumatically or electrically operated, axial or rotary, is that the flow through the cutting port is discontinuous, being interrupted when the cutting blade passes across the port. In vitreous surgery, this can often be observed as xe2x80x9cvitreous bounce,xe2x80x9d as the vitreous is alternately pulled into the port and released. This, in turn, can make removal of vitreous close to the retina hazardous, as the retina may become detached or may be inadvertently drawn into the cutting port.
Sussman and Zaleski, for example, provide one solution to this problem in U.S. Pat. No. 5,284,472. An alternative solution, however, is to increase the cutting rate. It is observed in clinical practice that the vitreous bounce is reduced to a negligible level when the cutting rate is high, generally in the range of 1200 to 1500 cuts per minute (cpm) or more. In U.S. Pat. No. 5,176,628, for example, Charles et al. state that increased cutting rate (up to 1200 cpm) is a desirable cutter characteristic.
Various improvements have gradually raised the maximum cutting rate of pneumatic axial guillotine cutters from 420 cpm in the 1970s to 600 cpm in 1982 and to 800 cpm in 1992. In contrast, high-speed cutting has been available from the very earliest electrically-operated guillotine cutters. Peyman and Dodich claim operation of an electric cutter at 3000 cpm in U.S. Pat. No. 3,776,238.
The principal reason for the slow progress with pneumatically-operated cutters is the physics of moving gas through a long interconnecting tube to drive the surgical handpiece. In order to preserve sterility in the vicinity of the patient and surgeon, the console containing the driver mechanism (which supplies the pneumatic energy to drive the cutter) is located at a considerable distance from the patient. The surgical handpiece is typically connected to the console through 72xe2x80x3 to 84xe2x80x3 of tubing. The rate at which the pneumatic pressure at the handpiece end of the tubing can change is limited by the physics of compressible-gas flow. In particular, the flow velocity through the tube cannot exceed the speed of sound.
Eight hundred cpm is not the ultimate speed limit for pneumatic axial guillotine cutters. A speed of 1500 cpm has been successfully demonstrated in a cutter positioned at the end of 84xe2x80x3 of tubing. To achieve this performance, however, requires coordinated improvements in both the surgical handpiece and the pneumatic driver mechanism in order to overcome the physical limitations of the intervening tubing.
While a high cutting rate is desirable for removing vitreous close to the retina, a high cutting rate is not desirable for removing material at other locations in the eye. The rate of removal of vitreous is significantly greater at a cut rate of 500 to 600 cpm than it is at a cut rate of 1500 cpm. This is because the vitreous is removed in xe2x80x9cnibblesxe2x80x9d at 1500 cpm and in xe2x80x9cbitesxe2x80x9d at 600 cpm. Thus, when vitreous bounce is not a concern, such as when removing material at the center of the eye, it is desirable to remove vitreous at a lower cut rate.
Despite the known benefits of having an adjustable-speed, pneumatic cutter that is also capable of operating at high speeds, few if any cutters exist that offer such functionality. Since high-speed choices are limited, some surgeons have resorted to using modern electrically driven probes even though they are expensive, heavy, and have a tendency to vibrate excessively.
Accordingly, there is a need for a vitreous cutter that can provide a high cutting rate, but retain as much as possible the advantages of the present pneumatically-operated vitreous cutters in terms of size, shape, weight, vibration, torque, low or minimal heat generation, and low cost.
In general terms, the invention provides a system having a pneumatically-operated axial guillotine cutter and a pneumatic driver mechanism that is capable of high-speed operation (at least 1200 cpm) with 84xe2x80x3 of intervening tubing. The pneumatic driver module or subsystem of the invention is suitable for incorporation into a vitreoretinal surgical system so as to provide a high-speed cutting function when used with an appropriate surgical handpiece. The invention also provides a pneumatic driver module suitable for attachment to an existing vitreoretinal surgical system so as to provide a high-speed cutting function when used with an appropriate surgical handpiece. The invention also provides a pneumatic driver module with a human interface for conveniently selecting one of two operating modes: a lower cutting rate for rapid removal of vitreous in the center part of the eye (a xe2x80x9ccutxe2x80x9d mode), and a higher cutting rate for more controlled removal of vitreous near the retina (a xe2x80x9cshavexe2x80x9d mode).
As noted, one embodiment of the invention is a subsystem or module to be incorporated into a surgical system. A very desirable alternative embodiment, however, is a free-standing module that could be purchased and attached to an existing vitreoretinal surgical system so as to upgrade the cutting rate without the necessity of replacing the entire surgical system in order to obtain this feature.
The present invention includes a system with a high-speed pneumatically-driven vitreous cutter, capable of operating at a cutting rate above 800 cpm, the maximum currently achievable with standard probes. In at least one embodiment, the cutter can operate at even higher speeds (above 1000 cpm), so that it can shave tissue. Because it has such capabilities, the cutter is referred to as a xe2x80x9ccut and shavexe2x80x9d or xe2x80x9cC and Sxe2x80x9d probe. In addition to high-speed functionality, the cutter or C and S probe can also be operated at peak pressure as low as thirteen (13) pounds per square inch (psi), an efficiency not previously achieved. Prior systems operated at pressures of about 20 to 30 psi.
The system includes a driver or actuator that powers the cutter. The actuator provides pressure pulses that can drive the cutter at cutting rates above 800 cuts per minute. The actuator is capable of supplying the appropriate pulses through an actuation or connection tubing of about 72xe2x80x3 to about 84xe2x80x3 in length. The actuator produces pulse trains at a frequency selectable by the user.
The invention may be implemented in one of two general forms. In the first form, the invention is implemented as a stand-alone or individual unit separates from a vitrectomy machine, phaco emulsification machine, or combined vitrectomy/phaco emulsification machine (generally referred to as a xe2x80x9csurgical machinexe2x80x9d). The inventors have developed at least two actuators that can take this form.
The first stand-alone actuator is designed to be attached to a surgical machine, such as a machine designed to operate a known 30 psi probe at a cut rate (frequency) of at least 600 cpm. The actuator of the present invention develops the pneumatic energy needed to operate a cutter at high speed by capturing the pneumatic output of the surgical machine. A waveform shaping circuit then controls a valve that converts the captured pneumatic energy into pulse wave trains to actuate the cutter (or C and S probe) at high frequencies. The actuator includes a human interface, which has input keys to allow a user to select the operating frequency of the cutter and a display to indicate the selected frequency and other conditions in the system.
The second stand-alone actuator is designed to be attached to a surgical machine that does not produce sufficient pneumatic energy to drive a cutter at high speeds. The second actuator develops its pneumatic energy using a pneumatic module having a small (typically less than 150 cubic inch or 2.5 liter), lightweight (less than 2 Kg), and low-noise compressor unit. A compressor control circuit drives the compressor motor only as hard as is required to produce pulse trains at the user-selected frequency.
One additional feature of both of the stand-alone embodiments is that the cutter on/off signal comes from the surgical machine. A further benefit of the stand-alone actuators is that no modifications or variations in the host surgical machine are required to operate the actuators.
The second method of utilizing the teachings of the present invention involves integrating an actuator module into a surgical machine. At least two types of actuators can be implemented in an integrated form. The first integrated embodiment is designed to be integrated into a surgical machine that uses an external pressure source. The external pressure source is then coupled to a pressure regulator within the actuator. The pneumatic energy appropriate for a high-speed cutter can be obtained through the regulator. A waveform shaping circuit is used to generate the pressure wave appropriate to actuate the cutter.
In the second integrated embodiment, the actuator in the surgical machine includes a small compressor. Thus, this embodiment does not require an external pneumatic power source. The cutting rate controls and the interface for adjusting the rate of cutting and displaying operational conditions of the surgical machine is modified to permit the display of the extended cutting frequency range of the cutter of the present invention. Like the other embodiments, a waveform shaping circuit is used to control the output valve to generate pulse trains used by the cutter.
No matter what form is used, each of the actuator embodiments contemplated may be used with a single, small, lightweight, pneumatic cutter or C and S probe.
As is apparent from the above, it is an advantage of the invention to provide an improved surgical cutter. Other features and advantages of the invention will be apparent by consideration of the detailed description and drawings.